Disclosed herein is a robust branched polyester resin that exhibits little to no degradation in solvent-free emulsification processes. Further disclosed is a branched polyester and process for preparing same, the branched polyester containing at least one of alcohol-derived branching sites or acid-derived branching sites that limit or prevent altogether degradation of the polyester during solvent-free emulsification processes such that the polyester exhibits less than about 20 percent molecular weight degradation following solvent-free emulsification. Further disclosed is a solvent-free emulsification process for preparing polyester latex wherein the polyester is the robust branched polyester described herein. Still further disclosed is a polyester latex prepared by a solvent-free emulsification process wherein the polyester is the robust branched polyester described herein.
There are many applications for polyester dispersions in the coatings and pharmaceutical industries. Examples of materials for which polyester dispersions can be required include paints, varnishes, powdered coatings, pharmaceutical additives, pressure sensitive adhesives, raw materials for toners, and raw materials for inks. Currently most polyester latexes are produced by a solvent-based approach which is not cost-effective, not environmentally friendly, and leaves undesirable amounts of solvent in the latex.
A solvent-free emulsification process has been developed that is cost effective, environmentally friendly, and produces latexes with no residual solvent. U.S. Patent Publication 2011/0028620A1, of Santiago Faucher, et al., entitled “Processes For Producing Polyester Latexes Via Solvent-Free Emulsification,” which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof a process for making a latex emulsion suitable for use in a toner composition including contacting a resin with a solid neutralizing agent in the absence of an organic solvent to form a mixture either via a co-feeding process or a pre-blend mixture, and adding a solid or aqueous surfactant to the pre-blend mixture or prior to melt mixing the mixture.
However, not all polyesters can be converted into latexes in a solvent-free process because certain polyesters suffer degradation in molecular weight as a result of the process. Previous toners comprising selected polyesters that account for about 60% of the toner particle mass can be emulsified by solvent-free emulsification without causing severe degradation of the polyester resin (that is, without causing a severe reduction of the molecular weight of the resin by chain scission events). Certain polyesters, however, degrade heavily, exhibiting, for example, a greater than about 60% decrease in molecular weight in a solvent-free process. It was originally believed that the higher molecular weight of these resins was the cause of degradation.
Solvent-free emulsification can provide an important, financially advantageous method for dispersion preparation. This is because the current solvent-based phase inversion emulsification process costs are high and equivalent to those of the resin itself. New resin designs that permit solvent-free emulsification are therefore highly desirable and will find applications for toners and in other fields of use.
Currently available resins are suitable for their intended purposes. However a need remains for an improved, robust, resin. Further, a need remains for polyester resins that exhibit minimal or zero degradation in solvent-free emulsification processes. Further, a need remains for polyester resins that exhibit minimal or zero degradation in solvent-free emulsification processes and resin dispersions (latexes) produced therefrom through solvent-free emulsification processes which resins can be used in a wide variety of industrial and other applications.
The appropriate components and process aspects of the each of the foregoing U.S. Patents and Patent Publications may be selected for the present disclosure in embodiments thereof. Further, throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.